@jhandley67 this looks like a Comcast decision to use the extra SSID capability to support their wifi hotspots instead of guest networks. Looks like Comcast expects their customers and all of the customer's guests to be Comcast customers so that any guests would automatically be able to use the wifi hotspots. I guess the thinking must be "Why would anyone invite non-Comcast users to their home?"
So, since Comcast doesn't support guest networks, looks like their licencee's can't have that capability as well.
I'll describe how it works for me. It's close to Eddiepet's diagram option 2, but the smart home devices are fully on the legacy WiFi. The Rogers Gateway is of course at the top, and it did not need any configuration. The second router has the guest WiFi capability. Log into the 2nd router and make sure the Wifi SSID is different from the Rogers gateway one, and that it's LAN address range is also different from the Rogers LAN range. This is normally already the case, as most personal routers are 192.168x.x and Rogers uses 10.0.0.x for its Local IP network. When you plug the 2nd router's WAN port into the Rogers Gateway LAN side, the 2nd router gets an address and gateway automatically, and in turn deals out WiFi addresses to your users in the 192.168 range and routes traffic to the Rogers Gateway. This is double NATing but should not require special configuration.
I just cancelled my Bell service to get Rogers and their router supported a guest WiFi. It NEVER occurred to me that internet provider supplied modem/router would not support in this day and age. My kids friends come to visit all the time with phones, laptops, tablets. I have network devices I do not want connected to my home network. Now I have to buy a real router and mess around with bridging and weird SSID configurations in the modem.
You can blame Comcast for that one. Comcast doesn't believe in Guest networks. All internet users in the U.S. are supposed to be Comcast customers (according to Comcast) so that they can use the modem hotspots that Comcast forces on its customers. That allows Comcast customers to roam wherever they want, and still have access to wifi. At least. so goes the theory. If you're not a Comcast customer, well, too bad.
Same story for licenced users like Shaw, Rogers, Cogeco (?) and numerous other ISPs. No guest networks for you....
Not this time around. The ignite gateway was installed by Rogers, and they configured it with a separate SSID, which is required by the TV boxes. WiFi users can choose the new SSID, which is supported by extenders so has greater range, or the old SSID.
"Not this time around" in my reply above refers to using bridge mode on the Rogers router (in response to darthwolf). In the past it was true that bridge mode was required to use a private home router, but the Ignite router now allows this with separate SSIDs, including guest mode (from the private router). Guests and IoT devices use the private router SSIDs, and home PC's etc. are on the Ignite router's SSID.
Double NAT is used, and there isn't any issue that needs solving. A private router on the original IP subnet is a solution to the Ignite Guest mode problem (yes it's a painful problem). It's just the burden of administering the private router and remembering that there are 2-3 subnets and 2-3 SSIDs.
It really is unbelievable that this modem doesn't have guest mode. 7-8 years ago I bought a D-link and it had one, yet this <2 year old modem (for me) doesn't.
I guess it's the definition of problem. For me, my old router settings didn't have to change, and it's WAN port connects to the Ignite router on the LAN side. Anything connecting to Ignite gets a 10.x.x.x address (including TVs and the old router), and anything connecting to the old one gets a 192.168.x.x address. The SSIDs are different so it's clear which one to use. Guest mode is a third SSID from the old router. This arrangement could be a problem if you decide to put non-guest hosts on different routers and they need to talk to each other. I have smart home/IoT devices on the old router, and PCs, printers and phones on the Ignite. Using a phone app to say control lights requires the old SSID, and say printing from the same phone would require the new SSID. Both connect to the Internet without any problems.
Almost 3 years since this complaint, but Rogers has not done anything to rectify this situation saying guest network is not part of this Ignite Modem. So it is safe to assume that they will continue to ignore this request.
I do not expect this to get implemented anytime soon, if ever... and the "they" that is the problem here is Comcast. Comcast upgrades the hardware in their gateways but any new features that they add to their software are pretty much limited to supporting new services that they can sell. Unfortunately, Comcast sees guest networks as a threat to their Xfinity WiFi hotspot service offering.